I don't think RMAH is killing the "Fair Play" gaming.
Because there's ALWAYS been Real Money trading over online games, and there's nothing any company can do about it. Unless they put a retina scanner for every time you log in, and still some crazy korean would steal some other people eyeball.
For example on WoW: With all that protection, people still trade gold, and people still sell whole accounts.
The difference is that as Blizzard noticed this problem is unavoidable, on D3 they decided to profit over it with a fee, providing some security over the trades.
As long as money exists, everything will be pay-to-win. From Online games, to Soccer matches and Wrestling...
Concerning RMAH... I hope Blizzard will keep it in their new games.
It has much potential if being used in a huge mmo with more to trade than just gear...
Think about rare pets, vegetables you farm, random trinkets you make etc...
I prefer the RMAH above ANY traditional cash shop from the developpers.
I hate these free to p(l)ay mechanics where you need to pay in a cash shop to have a bigger bag, more zones, better weapons ... ALL profits going 100% to those developpers.
At least RMAH is a trading where there is buying AND selling possible between players.
It is better than free to pay cash shops. period.